1. Field of the Invention
The present invention relates to an exhaust gas heat exchanger, an exhaust gas recirculation system having the exhaust gas heat exchanger, and an exhaust gas heat exchanging method.
2. Description of Related Art
Conventionally, for example, an exhaust gas recirculation system shown in FIG. 8 is known as a method to reduce nitrogen oxides (NOx) in exhaust gas from an internal combustion engine (specifically, diesel engine).
In this exhaust gas recirculation system 1a, intake gas is compressed (supercharged) by a turbocharger 20 and is cooled by an intercooler 30. Then, the intake gas flows into an internal combustion engine 10. Exhaust gas that outflows from the internal combustion engine 10 is discharged to an atmosphere after going through an after treatment apparatus 40. However, a part of the exhaust gas recirculates into the intake gas. In this case, there is no need for compressing the exhaust gas (i.e., no need for energy consumption by a compressing means), because the part of the exhaust gas flows into the intake gas on an upstream (low pressure side) of the turbocharger 20. Thus, fuel economy of the internal combustion engine 10 is limited from deteriorating.
However, in the above exhaust gas recirculation system 1a, nitric acid and sulfuric acid are generated when the NOx and sulfur oxides (SOx) in the exhaust gas are condensed. Thus, there is a fear of causing corrosion to the intercooler 30 and the turbocharger 20.